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Animal Transfer Stations Vs. Animal Handling Biological Safety Cabinets
Nov 11th, 2022
Important Distinctions in Airflow Fundamentals, Designs, Operational Techniques, and Intended Uses
In
the vivarium, protecting both personnel and animals must always remain top
priority. To ensure their protection, technicians must only handle animals within
proper equipment designed specifically for animal handling to avoid
cross-contamination. Animals may be immunocompromised or have specific pathogen
free (PDF) status making them susceptible to microorganisms and infections.Since
elimination and/or substitution of risk is rarely achievable in the vivarium,
engineering controls, administrative controls, and personal protective
equipment (PPE) provide the primary means of protection. Typically,
Animal Transfer Stations (ATSs) and Animal Handling Biological Safety Cabinets (AH
BSCs) serve the role of engineering controls in this context. Understanding the
capabilities and differences between these two controls will help eliminate unnecessary
costs and loss of resources due to compromised animals and research.
Key Operational and Design Fundamentals
Both
ATSs and BSCs utilize vertical laminar downflow of HEPA-filtered air inside the
work zone where the animals are being handled. HEPA stands for high efficiency
particulate air (filter). To comply with the National Sanitation Foundation’s (NSF)
standards, Class II biosafety cabinets must utilize HEPA filters that are at
least 99.99% efficient at 0.3 microns for the supply and exhausted airflow.
The constant downflow of air pulls dander and microorganisms straight down into
the air intake grills located on the bottom of the work zone. To extend the
lifespan of HEPA filters, washable mesh pre-filters are often employed to
remove larger particles, such as hair, dander, and dust, before reaching the
HEPA filters.Class II, Type A2 BSC downflow dynamics (shown right)On a Class II Type A2 biosafety
cabinet, ambient air will also be pulled into the inflow air grill at the
leading edge of the cabinet. These airflow dynamics are often
referred to as a dynamic air barrier, separating personnel from the product(s) inside
the work zone.
Although
both devices utilize similar airflow fundamentals, notable differences in
design, operational technique, and intended uses still exist between ATSs and
AH BSCs.Class II, Type A2 BSC inflow dynamics (shown right)
What is an Animal Handling Biological Safety Cabinet (AH BSC)?
A
Biosafety Cabinet (BSC) is an enclosed laboratory workspace for safely handling
potentially contaminated or otherwise hazardous materials requiring a
predefined level of biosafety. Because of the increased protection granted
by a BSC, personnel can practice procedural tasks in the work zone, such as
injecting, manipulating, or examining the product.
Three
different classes (I, II, or III) of biosafety cabinets currently exist, defined
by the varying degrees of biocontainment required. Class I cabinets are
designed to provide maximum protection of the operator and environment by
preventing outflow of pathogens or air-borne contaminants. Class II cabinets
provide mid-range protection while Class III devices offer the highest
containment with contents only accessible using physical barriers such as glove
boxes.
Multiple
types also exist within those classes, dictated by what proportion of the air
passing through the work zone gets exhausted or recirculated. Unlike
traditional BSCs designed for microbiology research, animal handling BSCs
accommodate the specific needs of animal researchers with unique modifications,
such as pre-filters, built-in waste chutes, and/or cage pass-through chambers.
The higher level of containment provided by biosafety cabinets protect animals that
may be immunocompromised, biohazardous, or designated as unknown infection
status.
NuAire LabGard® ES NU-677 Class II, Type A2 Animal Handling
Biosafety Cabinet (shown right).
Diagram of various classes and types of BSCs and the inflow and outflow patterns of air movement (shown above).
What is an Animal Transfer Station (ATS)?
Animal transfer stations (ATSs) are clean air workstations
specifically designed to accommodate changing of cages for non-infected animals
only. ATSs are designed for transferring animals between dirty and clean cages
and are not typically intended for procedural work, such as injecting,
handling, performing experiments, etc. They provide protection against most allergens but do not ensure
protection against exposure to infectious agents. Although no specific
containment performance standards and/or certifications currently exist, ATSs
must be certified to operate according to manufacturer specifications.
NuAire AllerGard® NU-621 Single Sided Animal Transfer
Station (shown right)Most
ATSs utilize a “push-pull” downward airflow pattern. An air supply impeller at
the top of the cabinet creates the “push” action by directing air straight down
through the work zone while a second motor beneath the work surface “pulls” the
air through the air slots located on the edges of the work surface. Due to the lack of regulatory agencies, ATSs can
vary widely in design and functionality. However, as mentioned, one must still
regularly certify the ATS functions according to manufacturer specifications.The
ATS workspace can be accessible from one or two sides, depending on the intended
usage. Typically, one-sided stations create a stronger air barrier than their
dual-sided counterparts. Two-sided ATSs offer greater convenience, but the
additional access opening increases the surface area of the air barrier, making
it markedly less stable.
The
opening sash levels can be higher than biosafety cabinets, allowing for large
cages to be moved in and out of the work zone with ease. ATS units typically
occupy a smaller footprint and can be conveniently moved between animal IVC
racks and handling rooms. The versatility of these devices makes them suitable
for widespread, low-risk workflows throughout the vivarium.NuAire AllerGard® NU-620 Dual Sided Animal Transfer Station (shown right)
What are the Regulatory Considerations of AH BSC Devices?
Design features of Biosafety
Cabinets are largely dictated by performance standards such as NSF/ANSI 49 or EN
12469. These standards involve multiple aspects of BSC operation and include: downflow
and inflow velocities (dynamic air barrier), allowable sash heights, biological
containment restrictions, and exhaust system parameters. Although not a strict
requirement, animal handling models typically utilize a pre-filter to catch
hair and dander in line with HEPA filtration.
Additional considerations
include recertification requirements upon moving the BSC unit and/or operating
the cabinet in different locations throughout the vivarium. Proper cabinet
operation should be confirmed by airflow smoke pattern tests at each site of
use. If the cabinet is relocated to another facility or subjected to excessive
shock/vibration, the BSC should be recertified to ensure proper containment.
Diagram of Class II, Type A2 Biosafety Cabinet Airflow
Dynamics (shown right)Biosafety cabinets must be
routinely recalibrated and certified to regulatory agencies’ specifications. This
includes ensuring the standard inflow and downflow velocities dictated by the
NSF are maintained.
For Class II BSCs, the
inflow velocity should be a minimum of 100 fpm (0.51 m/s)Downflow velocity
requirements vary by model and are typically 50 to 80 fpm (0.25 to 0.40 m/s)
average for both typesClass II, Type A2 BSC models
exhaust approximately 30% of the air passing through the work zone, while
recirculating the other 70%Class II, Type B1 cabinets
are the inverse of A2 models by exhausting 70% and recirculating 30% of the air
passing through the work zoneClass II, Type B2 and Class
III BSCs exhaust 100% of all air passing through the work zone
What are the Regulatory Considerations of ATS Devices?
Diagram of Animal Transfer Station Airflow Dynamics (shown right)Due
to the absence of ATS regulatory agencies, device manufacturers set the
performance standards of their respective animal transfer stations. Single-sided
ATSs offer allergen protection through a dynamic air barrier through the front
opening of the workstation. HEPA-filtered air gets pulled from the top of the
device and flushes the work zone. Overall, ATS
units tend to have marginally lower velocities, but this will also vary greatly
between manufacturers. It is absolutely imperative to communicate with the
manufacturer before choosing a specific model that meets the needs of the lab.
Summary
Animal Transfer Stations are generally suited for lower-risk duties such as cage
changing, while Animal Handling Biosafety Cabinets provide higher levels of
security for use with infected animals and biocontainment applications
including blood sampling, biopsies, and other invasive procedures. The
infection status and whether the animal is immunocompromised will influence the
type of containment system required. Although they may appear similar, each type
of device requires specific training, routine certification, and due diligence
during the purchasing process. Use of safe practices and strict adherence to
standard operating procedures (SOPs) should be always maintained to mitigate potential
risks.
This
editorial is published in partnership with Nuaire.
References:
1. National
Institute for Occupational Safety and Health (NIOSH) Hierarchy of Controls
2. NSF/ANSI
49-2019 Biosafety Cabinetry: Design, Construction, Performance, and Field Certification
